1. Field of the Invention
The invention relates to a projecting device, and more specifically, to a projecting device for displaying electrical images.
2. Description of the Prior Art
Please refer to FIG. 1. FIG. 1 is a perspective view of a prior art projecting device 10 of an LCD projector. The projecting device 10 comprises a light source 12 that produces a white light beam, a uniform illumination optical device 14 installed in front of the light source 12 for converging the white light emitted from the light source 12, into a uniformly distributed rectangular light beam, a light separating device 16 for separating the rectangular light beam into red, green and blue color input light beams, a trichromic prism 18 having three input sides and an output slide for synthesizing the three input light beams into an output light beam, three modulating panels 20 each formed by a monochrome liquid crystal panel and separately installed in front of the three input sides of the trichromic prism 18 for modulating the three input light beams, three focusing lenses 17, 19 and 21 separately installed in front of the three modulating panels 20 for focusing the three input light beams from the light separating device 16 onto the three modulating panels 20, and a projecting lens 22 installed in front of the output side of the trichromic prism 18 for projecting the synthesized output light beam from the trichromic prism 18 onto a screen 24. Each of the modulating panels 20 is formed by a transparent monochrome liquid crystal panel for displaying a monochrome image. The is trichromic prism 18 synthesizes the three monochrome images to form the output color image.
The light separating device 16 comprises a first dichroic mirror 26 for separating the red light from the rectangular light beam, a reflecting mirror 27 for reflecting the red light from the first dichroic mirror 26 onto the focusing lens 17, a second dichroic mirror 28 for separating light reflected from the first dichroic mirror 26 by reflecting blue light to the focusing lens 19, and two optical lenses 30 and two reflecting mirrors 32 for passing and reflecting green light to the focusing lens 21. FIG. 1 clearly shows that the distance traveled by the green light is much longer than that of the red and blue lights. Since traveling distances affect light intensities, the two optical lenses 30 installed in front of the two reflecting mirrors 32 are essential to converge the green light so as to compensate for the loss of its light intensity.
However, the installation of the two optical lenses 30 makes a structure of the light separating device 16 complicated and costly. It is therefore an important objective to provide a projecting device with a simple structure that can solve the problem of unequal traveling distances for the three color beams.
It is therefore a primary objective of the present invention to provide a projecting device to solve the above mentioned problem.
Briefly, in a preferred embodiment, the present invention provides a projecting device comprising:
an illumination device for emitting a polarized trichrome light comprising three primary colors with various polarization;
a first, second and third modulating device, each modulating, reflecting, and changing the polarization of its own distinct polarized monochrome light;
a light separating device having a first dichroic mirror, a first polarization beam splitting mirror, a second polarization beam splitting mirror, and a third polarization beam splitting mirror, the first dichroic mirror and the third polarization beam splitting mirror being arranged along a first diagonal direction, and the first and the second polarization beam splitting mirrors being arranged along a second diagonal direction perpendicular to the first diagonal direction; and
a first retarder film installed between the second and the third polarization beam splitting mirrors; wherein the first dichroic mirror separates the polarized trichrome light into a first polarized monochrome light and a polarized dichrome light, and transmits these two lights separately to the first and second polarization beam splitting mirror, the first polarization beam splitting mirror transmits the first polarized monochrome light to the first modulating device and transmits the modulated light reflected from the first modulating device to the third polarization beam splitting mirror, the second polarization beam splitting mirror separates the polarized dichrome light into second and third polarized monochrome lights which are directly transmitted to the second and third modulating devices, and then transmits the modulated lights reflected from the second and third modulating devices to the third polarization beam splitting mirror through the first retarder film, and the first retarder film changes the polarization of one of the modulated lights reflected from the second and third modulating devices, the modulated lights transmitted from the first and second polarization beam splitting mirrors are synthesized by the third polarization beam splitting mirror to form an output light beam.
It is an advantage of the present invention that the projecting device has a very simple structure.
It is another advantage of the present invention that the traveling distances of the three polarized light beams. are approximately equal and shorter than that of the prior art device.
These and other objects and the advantages of the present invention will no doubt become obvious to those of ordinary skill in the art after having read the following detailed description of the preferred embodiment that is illustrated in the various figures and drawings.